Comment # 1 on bug 949983 from Wolfgang Rosenauer

I don't know enough about the appdata (and also mimehandler) stuff but also
cannot remember that I really did anything special with that.
The same package of Firefox is provided for several distributions starting with
12.3 or so and I have never seen that issue.
So I would prefer to have the underlying issue fixed (whatever that is) rather
than fixing in Firefox.
But then again if it's just about adding something like

   Provides: appdata(firefox.appdata.xml)

(would it look like this?)
then it would probably be fine.